A sample qualitative experiment using only gas chromatographic analysis is adapted to inject, for example, a sample desired to be qualified, and a compound as a reference substance, which is expected to be the sample desired to be qualified, into a column with a syringe or the like, and compare respective retention times that are times required for a detector to detect constituents of them. For example, in the case where the respective retention times regarding the constituents are coincident with each other, it can be identified that the sample desired to be qualified is identical to the reference substance.
Meanwhile, a retention time is influenced by a parameter such as a column length or linear velocity of carrier gas, and therefore even if a sample desired to be qualified is coincident with an expected reference substance, in the case where different gas chromatographs or different experimental conditions were used to made measurements, respective retention times are different. That is, in such a case, even in the case of comparing the two retention times with each other, a quality determination cannot be made.
For this reason, in order to be able to prevent the influence of the parameter as described above, and qualify of a substance desired to be qualified, retention indices are compared with each other. To describe more specifically, a retention index is one that is not influenced by many of experimental conditions in gas chromatographic analysis as compared with a measured value such as a retention time, and easily made to serve as a target for comparison at the time of quality determination. For this reason, for example, NIST and the like collect a number of retention indices for each compound, and organize them as a library, and a retention index of a registered substance that is stored in the library and expected to be a sample desired to be qualified, and a retention index that is actually measuring on the sample desired to be qualified are compared with each other to make a quality determination (see Non-patent Literature 1).
Meanwhile, although not being influenced by a column length, linear velocity, or the like, if temperature conditions such as a setting temperature at the time of perform gas chromatographic analysis are different, even retention indices respectively take different values. For this reason, in the case of actually measuring a retention index of a sample desired to be qualified, a retention index of a reference substance expected to be the sample desired to be qualified, which is included in the library, and a temperature condition at the time when the retention index in the library was actually measured are preliminarily obtained, and the temperature condition is set for a gas chromatograph to actually measure the retention index of the sample desired to be qualified.
However, in the case where a sample desired to be qualified is an unknown sample of which composition and the like cannot be expected at all, which registered substance registered in the library should be referred to be unknown, and therefore a temperature condition at the time of performing gas chromatographic analysis cannot be determined in advance. In addition, the temperature condition of the gas chromatographic analysis is appropriately changed for each registered substance, or depending on specifications of a system for the analysis, separation accuracy of a desired constituent, or the like, and therefore retention indices registered in the library are actually measured in various temperature conditions. Accordingly, even in the case of, for the unknown sample, setting a temporary appropriate temperature condition to actually measure a retention index, and using the actually measured value to search the library, a retention index of a registered substance completely irrelevant to the unknown sample is extracted, or other result is obtained, and therefore it is very difficult to identify the unknown sample. In other words, in the currently used retention index library, it is possible to uniquely search for a retention index from a registered substance name; however, in the case of reversely searching a registered substance name or the like from a retention index, a plurality of registered substances are outputted, or in some cases, nothing is outputted because a coincident retention index is not present in the first place. Accordingly, it is considered that even in the case of identifying the unknown sample only by the gas chromatographic analysis, the number of uncertainties is large, and therefore certain identification cannot be made. As evidence of this, for identification of an unknown sample of which identity cannot be expected at all, not only the gas chromatographic analysis, but other analysis such as mass analysis like GC/MS analysis or the like is also typically performed together.
In addition, as a way to handle the case where a temperature condition in the gas chromatographic analysis is different, as disclosed in Patent Literature 1, converting a measured retention time to a retention time, which is registered in the library and under a temperature condition under which the retention time was measured, to make a quality determination is described; however, a method for converting some retention index to a retention index under a predetermined temperature condition is not described as expected. That is, up to now, a method that can qualify an unknown sample even in the case where a parameter such as a temperature condition or linear velocity is different has not been known.